Overhead maintenance apparatus



Jan. 24, 1967 J. s. HUBBARD 3,

OVERHEAD MAINTENANCE APPARATUS Original Filed Oct. 31, 1963 4Sheets-Sheet 1 "'l /6 l[ mm luu I NVENTOR.

Jan. 24, 1967 J. s. HUBBARD 3,299,983

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United States Patent Office 3 199,983 Patented Jan. 24, 1967 3,299,983OVERHEAD MAINTENANCE APPARATUS John S. Hubbard, R.R., Parker, Ind. 47368Original application Oct. 31, 1963, Ser. No. 320,329, now Patent No.3,224,528, dated Dec. 21, 1965. Divided and this application June 28,1965, Ser. No. 476,226 Claims. (Cl. 182-63) This application is adivision of my copending prior application Serial No. 320,329, filedOctober 31, 1963, now Patent No. 3,224,528 entitled Overhead MaintenanceApparatus.

The present invention relates generally to apparatus for overheadmaintenance work in industrial plants and elsewhere, and particularly toapparatus capable of raising one or more workmen to elevated positionsat which the workmen may clean, repair or otherwise service suchoverhead equipment as light fixtures electrical systems, sprinklersystems, water, steam, air and oil lines, conveyor systems, ventilatingand heating systems, and the like.

Two problems with existing overhead maintenance apparatus are that theyare too bulky for use in the narrow aisles of many plants and that theylack sufficient mobility to service many hard-to-reach and relativelyinaccessible places. Thus, in many operations the presently knownoverhead service equipment cannot be employed; and instead, uneconomicaland slower access equipment, such as scaffolding and ladders, must beused.

Accordingly, it is one object of this invention to provide overheadmaintenance apparatus having a column or mast supporting a lift platformwhich is capable of carrying one or more workmen and which whenpositioned at the upper terminus of the supporting mast is movableoutward from and above the mast.

It is a further object of this invention to provide overhead maintenanceapparatus having a lift platform which is movable farther outward fromthe remainder of the unit than the platforms of the overhead maintenanceequipment presently known.

It is another object of this invention to provide overhead maintenanceapparatus having a lift platform which is movable throughout a greaterarea than the platforms of the overhead maintenance apparatus presentlyknown.

It is also an object of this invention to provide overhead maintenanceapparatus having a lift platform which is rotatable about an axisperpendicular to the horizontal plane of the base.

It is another object of this invention to provide overhead maintenanceapparatus having a lift platform with sufficient mobility to facilitateservicing of hard-to-reach and relatively inaccessible places.

A still further object of this invention is to provide overheadmaintenance apparatus having a lift platform which is sufiicientlymobile so as to permit servicing of a maximum number of locations withminimum movement of the base.

Another object of this invention is to provide apparatus which greatlyenhances the efficiency and substantially reduces the cost of repairing,maintaining, and installing overhead equipment in industrial plants.

Another object of this invention is to provide apparatus which may bereadily adapted for and greatly improves the efficiency of such outdoormaintenance operations as the servicing and repairing of street lightingfixtures.

Still another object of this invention is to provide apparatus which iseasy and economical to operate and relatively inexpensive to maintain.

Additional objects will be manifest from a consideration of thedrawings, description, and claims.

In accordance with one embodiment of this invention, overheadmaintenance apparatus is provided having a base, preferably a mobile,self-propelled truck or the like, a turntable mounted on the base androtatable relative to the base, and an extensible vertical mast or liftcolumn mounted on the turntable and rotatable therewith. A platformcapable of carrying at least one workman is connected to the upper endof the mast, preferably by means of an arm which is pivotally connectedboth to the mast and to the platform. The platform is so arranged withregard to the remainder of the apparatus that it will remain in asubstantially horizontal plane regardless of the angular position of themast and arm. This arrangement permits the platform to be maneuveredaround various equipment and piping and into small openings, many ofwhich would be inaccessible when presently known methods and apparatusare employed.

For a more complete understanding of the present invention, drawingshave been provided as follows:

FIGURE 1 is a perspective view of one embodiment of the presentinvention.

FIG. 2 is a back view of the embodiment of FIG. 1 showing only the mastand arm with the actuating mechanism of the arm exposed.

FIG. 3 is a perspective view of the actuating mechanism of the arm ofthe embodiment of FIG. 1.

FIG. 4 is a fragmentary perspective view of a modification of theplatform and mast assembly shown in FIG. 1 and portions thereof cutaway.

FIG. 5 is similar to FIG. 4 but showing another modification of theplatform and mast assembly of FIG. 1.

FIG. 6 is similar to FIG. 4 but showing a third modification of theplatform and mast assembly of FIG. 1.

FIG. 7 is a fragmentary side view showing a modification of theembodiment of FIG. 1 and showing, in dotted lines, the arm thereof invarious positions.

FIG. 8 is a fragmentary side view of the arm and platform of FIG. 7illustrating the actuating mechanism of the arm in detail.

FIG. 9 is a bottom view of the arm and platform assembly of FIG. 8,showing the two parallel sections of the arm in detail.

FIG. 10 is a fragmentary side view illustrating a modification of FIG. 5in which the mast is mounted on a turntable and the platform is shown invarious positions relative to the base of the apparatus.

Referring now to FIGURE 1, one preferred embodiment 10 of the presentinvention is illustrated. The apparatus includes generally a suitablebase 11, a turntable 12 mounted on the base and rotatable relativethereto, a telescoping mast 13 mounted on the turntable 12, and abattery box 14 containing a storage battery 19 and a counterweight 20also mounted on the turntable. An arm 15 is pivotally connected at oneend to a supporting member 21, extending at right angles from the mast13 and forming a part thereof. The arm 15 is also pivotally connected atits other end to a platform support 16 on which a platform 17 ismounted. The arm 15 may be adjusted to pivot in a vertical plane throughan arc of approximately 180 degrees, and is also adapted to move about avertical axis together with the mast through an arc of 360 degrees. Thebase 11 is preferably any one of the self-contained, self-propelled,mobile types known to the art. It is preferably battery powered andsupported by two drive wheels and two steering wheels 72. The

turntable 12 may be of any suitable conventional design and is poweroperated and preferably torque controlled. Besides supporting the mast13 and the battery compartment 14, the turntable may also supportcontactors and a fuse panel. The mast 13 is a conventional telescopingtype, preferably having three or more sections. It may be actuated by ahydraulic cylinder through dual mechanical linkage having anti-frictionguide bearings at load points. The hydraulic pump may be a conventionalelectrically operated gear type controlled by an electrically operatedvalve and flow regulator. In the embodiment of FIG. 1 the mast sectionhaving the smallest diameter is on the bottom and the one with thegreatest diameter is at the top (See FIG. 2).

Examples of a suitable turntable, turntable arrangement with respect tothe base, and telescoping mast will be found in United States LettersPatent No. 3,095,945, issued July 2, 1963 to M. E. Mitchell.

The mast 13 and battery box 14 are each mounted on the turntable 12offset from the central axis thereof and are diametrically opposite eachother. The turntable 12 is U-shaped, i.e., it is provided with twoU-shaped flanges 18 which extend upward from the turntable 12 andsupport the battery compartment 14. Compartment 14 contains a battery 19and a counterweight 20' which provides the necessary stability for theunit when the arm 15 and attached platform 17 and moved through theirvarious positions of adjustment. The battery box 14 generally extends toa position outside the flanges 18 and the counterweight 20 is disposedin the portion of the box 14 which is outside the flanges 18. Thebattery 19, on the other hand, is generally positioned in that portionof the box between the flanges when used with a counterweight. Thebattery 19, in addition to supplying electrical power for'operation ofthe unit 10, also acts as a counterbalance, and in some operations maybe used alone as a counterweight. In such operations it is desirable tomount the battery in the outermost portion of battery box 14 so that thebattery will be disposed at a greater distance from the center of theturntable 12 and from the mast 13. In this way the battery may act as amore effective counterbalance. In certain modified constructions of thepresent invention, the mast 13 may be disposed coaxially to the axis ofrotation'of the turntable 12.

The arm 15, best shown in FIGS. 2 and 3, is actuated by a hydrauliccylinder through dual mechanical linkage. The arm 15 comprises a frame22, a hydraulic cylinder 24 welded or otherwise connected to the frame(FIG. 2 shows the cylinder 24 connected to the frame 22 by members 25and 27), a piston 26 for movement within cylinder 24, and a trunnion 28attached to the piston 26. The trunnion 28 is attached to twopredetermined lengths of roller chain 30 which pass over four fixedsprockets 32. Two of the sprockets are'secured to the mast portion 21 bybolts 34, and the other two are held to the platform support 16 by bolts36. The frame '22 is attached at each end to bushings 38 which rotateabout fixed shafts secured to the supporting member 21 and the platformsupport 16. A pump 40, actuated by an electric motor 42, forceshydraulic fluid from a supply tank 44 through a four-way solenoid valve48 and into the hydraulic cylinder 24. Depending upon the position ofthe movable part of valve 48, fluid is either directed through hydraulichose 50 to the upper part of the cylinder 24 or through hydraulic hose51 to the lower part of the cylinder, and the piston 26 is accordinglyactuated inward or outward. When the piston is moved, it actuates thetrunnion which in turn applies a force on the chain 30, causing thechain to wrap and unwrap about the sprockets 32 and thereby actuate thearm 15. Thus, if the piston is forced outward, it actuates the trunnion28 away from the cylinder 24 and causes the trunnion to apply a force onthe chain 30 which lowers the arm 15. If the piston is depressed, thetrunnion 28 is moved toward the cylinder, applying an opposite force onthe chain 30, which raises the arm 15.

Travel of the arm 15 is regulated by the length of the cylinder stroke.Thus, a shorter cylinder stroke is used to reduce the distance in whichthe arm and attached platform travel in a vertical plane. This shorterstroke is accomplished by inserting stop tubes in the existing cylindersor by using a shorter stroke cylinder. The rate of speed of the arm 15is controlled by flow resistors disposed in the hydraulic hoses 5t) and51 at the points where the hoses connect with cylinder 24. Theseresistors regulate the rate of flow of hydraulic fluid to cylinder 24and provide a safety feature by preventing the arm 15 from falling inthe event one or both of the hoses 50 and 51 break.

It is important that the chains 30 are sufiiciently taut, and the lengthof the chains may be adjusted by altering the thickness of shims 52(best shown in FIG. 2) which are positioned between plate-s 54 (seeFIGS. 2 and 3) and trunnion 28. Chain length may also be adjusted bybreaking the chain and employing a turnbuckle to secure the broken ends.Operation of the turnbuckle will then adjust the length of the chains.

Although valve 48 is preferably a four-way valve, a three-way valveor atwo-way valve in combination with a check valve may be used in lieuthereof. If twoor three-way valves are used, only one hydraulic linewould connect the valve 48 to the cylinder 24 and the fluid would beintroduced at the bottom of the cylinder. The fourway valve is moredesirable than the other valves because when using the latter valves,gravitational, rather than hydraulic, force is used to lower the arm 15from a raised position. Hydraulic force is only utilized to raise thearm. Thus, when the arm 15 is adjusted to a position degrees from itsretracted position, i.e., when the platform is at its uppermost positionrelative to the mast, the torque created by the weight of arm 15 may beinsufficient to actuate it downward. Thus, to lower the arm from such aposition the operator would have to initiate the downward movement bypushing the arm 15 by hand or otherwise.

The pump 40 is a conventional gear-type, which is probably the mosteconomical, but it may be a vane-type or piston-type pump. The motor 42actuating the pump is a typical series wound 12, 24, or 36 volt electricmotor. Electrical power is supplied to the motor 42 from the battery 19.Current from battery 19 is transmitted through coil cord 56 to terminalbox 57, then to terminal box 58, and from there to the motor 42. Thecoil cord 56 is used because it extends and retracts in correspondencewith the extension and retraction of the mast 13. When the mast isretracted, the excess cord 56 is contained in the cord receptacle 59.Any conventional hydraulic hose or flexible tubing 50 and 51 may be usedto transport the hydraulic fluid to the various parts of the hydraulicsystem. The pump and motor referred to earlier for operating the mastare the same kinds as those used to operate the arm. In someapplications only one pump and motor may be used to operate both the armand the mast.

In the present invention, electrical energy for operating the hydraulicsystem may be supplied by a generator driven by an internal combustionengine, rather than by the battery 19; and, when the mobile base 11 is ahighway truck, the hydraulic system may be driven by a power take-offfrom the truck engine, rather than bythe battery 19.

The platform 17 is mounted on a platform support 16 which is secured toone end of arm 15. The platform generally comprises a floor 60, railingsupports 62, and safety railings 64. The platform should be large enoughto support at least one man. It should also be of such dimensions thatit will contribute to the compactness of the overall unit.

The platform 17 may be fixed to the platform support 16, as shown inFIG. 1, or it may be connected in several other ways, as shown in FIGS.4, 5, and 6.

FIG. 4 shows a modified platform unit 82 which could be substituted forthe platform shown in the embodiment of FIG. 1. It will be noted thatthe modification 82 of FIG. 4 does not utilize an arm 15 like the oneillustrated in FIG. 1 and described above. Such modification, however,could be combined with the arm 15. The modification 82 comprises asupport 84 which is either welded or bolted at one end to the mast 13and forms a part thereof and which extends outward from the mast 13forming a right angle therewith. Mounted on the support 84 adjacent thedistal end thereof is a turntable assembly 85, and mounted on theturntable assembly 85 is a platform 90. The platform should besufficiently spaced from the mast 13 so that the platform may rotatewithout interferenoe from the mast when the latter is fully retracted.The turntable assembly 85 comprises a turntable 86 secured' to a toothedbearing 87 by bolts 88. The bearing 87 is attached to the support 84 andthe turntable 86 is connected to the platform 90. The turntable 86 is actuated by an electrically powered motor 94, which drives a chain andsprocket assembly connected to bearing 87. The latter assembly comprisessprocket 95 and roller chain 96 and is connected to motor 94 through agear box 97, a V-belt 98, and V-pulleys 99 and 100.

FIG. 5 shows another modified platform unit 102. In this embodiment theunit 102 is provided with a support 104 welded, bolted, or otherwisejoined at one end to the mast 13. If desired, the support 104 could beconnected to the mast by means of an arm similar to the arm 15 of theapparatus of FIG. 1. The support 104, like support 84 of the embodimentof FIG. 4, extends outward from mast 13 at right angles thereto. Mountedon support 104 is a platform 106, which is adjustable outwardly andinwardly relative to the mast 13 along the fixed support 104. Since theplatform 106 may be moved outward a substantial distance from mast 13,the servicing of normally hard-to-reach places is greatly facilitatedwhen this platform unit is used. Movement of platform 106 is effected byan ordinary 12 or 24 volt series wound electric motor 108 which drives arotatable shaft 110 connected to the motor by means of a V-belt 112, V-pulleys 113 and 114, and a gear box 116 in which the gear ratio is about30:1. Attached to each end of the shaft 110 and rotatable therewith aresprockets 118 which engage roller chain 120. The chain 120 is secured ateach end to the extreme ends of platform 106 so that when the sprockets118 rotate, the platform 106 moves relative to the support 104. Camfollowers or roller bearings 122 secured to each side of the support 104by nuts 124 are provided for supporting the platform 106. The camfollowers will rotate as the platform travels relative to support 104. Acontrol panel 160, which will be hereinafter explained in greaterdetail, is mounted on the platform 106 for controlling movement of theplatform, the mast, and the base.

FIG. 6 shows a further modification of the platform. In this embodimenta platform unit 130 is provided having a support member 132 and aplatform 134. The support member 132 is rotatable about the verticalaxis of the mast 13, which may be a telescoping type, through an arc of360 degrees. In lieu of the embodiment shown in FIG. 6, a suitablearrangement may be employed in which an arm similar to the arm 15 shownin FIG. 1 is used. Thus, the platform may be rotated to a position whereit is in registration with the base so that no part of the platform willoverhang the base. The platform may be manually driven although theillustrated embodiment shows the platform driven by an electric motor136. Fixed to the underside of the support 132 is a sprocket 138. Thissprocket engages roller chain 140, which in turn engages anothersprocket 142; the latter sprocket being driven by electric motor 136connected thereto through a V-belt 144, V-pulleys 146 and 148, and agear box 150 in which the gear ratio is approximately 100:1. A supportbearing collar, not shown, which is located immediately below sprocket138 and is fixed to mast 13, retains the platform unit at a fixed heightrelative to the top portion of the mast.

Referring again to FIG. 1, mounted on one of the railing supports of theplatform 17 nearest the mast is a control pane-1 160, which contains theelectrical controls for positioning the various components of the unit10. Thus, while standing on the platform 17, an operator may regulatemovement of the arm 15, platform 17, mast 13, turntable 12, and base 11.The control panel may include a four position Joy Stick control 162 forregulating movement of the arm 15 and platform 17, a 2-position levertype control for regulating upward and downward movement of the mast 13,and a push-pull emergency control for cutting off the electrical powerregulating the upward movement on the arm and mast, and all movement ofthe base and turntable. Also, the panel may contain a lever-typemulti-position base travel and turntable control and a key-operatedon-off switch.

Besides the controls located on the platform, there is a steeringcontrol 74 for regulating the direction of travel of the base. Thesteering control 74 operates the front wheels 72 through conventionalmechanical steering linkage. Other controls may include automatic limitswitches for preventing movement of the base when the mast or arm is inan extended position.

FIG. 7 illustrates a modification 200 of the apparatus 10 shown inFIG. 1. In unit 200 the mast 202, unlike the mast 13 of unit 10, ismounted directly on the base 204, rather than on a turntable, and isinclined rearwardly. Even though the mast 202 is not disposed on avertical axis or on an axis perpendicular to the base 204 of theapparatus, it operates in substantially the same manner as the mast 13shown in FIG. 1. The angle of inclination of mast 202 will vary fromless than 1 to about 20 with respect to its vertical axis. By incliningthe mast rearwardly, greater rearward reach is provided without thenecessity of increasing the length of the offset arm 206 connected tothe mast or the pivotal arm 208 at tached to the oflfset arm. A furtheradvantage is that, when the mast is fully retracted and the pivotal arm208 is positioned in its forwardly extending direction (as shown indotted lines in FIG. 7), the platform 209 secured to the outer end ofthe pivotal arm will be positioned in registration with a part of thebase 204, so that portions of the platform will not project forwardly ofthe base.

The offset arm 206 is connected to the upper end of mas-t 202 anddisposed in a plane substantially parallel to the plane of the base 204.The pivotal arm 208 is secured to the distal end of this offset arm 206.The pivotal arm 208 is similar to the arm 15 of the embodiment 10 ofFIG. 1, except that it is split into two identical parallel sections 210and 212 (See FIG. 9). Each section of arm 208 operates on the sameprinciple as arm 15 and consists of the same component parts as thatarm. Thus, section 210 comprises a frame 214, a hydraulic cylinder 216,a piston 218 for movement within the cylinder, a trunnion 220 connectedto the exposed end of the piston, and roller chain 222 connected to thetrunnion and passing over two sets of sprockets 224, 226, 228, and 230.Sec tion 212 of arm 208 is constructed in the same manner as section210.

Arm section 210 is attached to a bearing 232 (see FIG. 9) which isrotatably mounted on a shaft 234 (see FIG. 8), the latter being securedat one endto sprocket 228 and at the other end to sprocket 230. Sprocket230 is secured to the outside surface of ofiset arm 206. Arm section 212is similarly connected to a bearing 236 which is also mounted on ashaft, such shaft being secured at its opposed ends to sprockets 238 and240. Sprocket 240, like sprocket 230, is secured to an outside surfaceof offset arm 206.

Since the sections 210 and 212 are attached to the outside surfaces ofthe offset arm 206, the pivotal arm may be adjusted to :aforwardsubstantially horizontal direction in which the upper portion of themast 202 and the offset arm 206 are disposed between the sections. Theouter ends of the sections 210 and 212 are pivotally connected tobrackets'241 and 242 depending from the central axis of the platform209. Bracket 241 is secured to sprocket 226, and bracket 242 is securedto sprocket 245. Arm sections 210 and 212 are connected to bearings 246and 247, respectively, and the bearings are rotatably mounted on shaftsjoined at each end to the sprockets.

.Thus, bearing 246 is mounted on shaft 248 (see FIG. 8),

joining sprockets 224 and 226, and bearing 247 is mounted on a shaftjoining sprockets 244 and 245. Here, again, the sections are connectedrelative to the outer surfaces of the platform so that the platform maybe adjusted to a forward position in which a portion of the platform isdisposed between the arm sections.

The structure 200 illustrated in FIG. 7 does not include a turntable,and the inclined mast 202 is accordingly not rotatable relative to thebase. Where an inclined mast is used, there is considerable overhang ofthe platform in certain positions of adjustment, and to maintainstability of the entire device it is necessary to position the batteryand the counterweight a greater distance from the mast'and generallyadjacent the end of the base opposite the end closest to which the mastis disposed.

In unit 200, battery 250 and counterbalance 252 are immediately adjacentthe forward endof base 204. To mount the battery and counterbalance on aturntable in this embodiment would require a turntable of such diameterthat the entire structure would be of an impractical width for normaloperations. And, of course, to provide for the rotation of the mast on aturntable without having is less than 10 degrees, however,- it ispossible to position the mast on a turntable even without such acounterbal- "ancing weight thereon.

FIG. 10 shows an embodiment 260 in which an extensible mast 262 isslightly inclined and ismounted on a turntable 263. Diametricallyopposed to the mast is a battery box 264 containing a battery 266 and acounterbalance 268. The operation and structure of the unit 260 of FIG.10 are identical to unit 200 illustrated in FIG. 7, except that the unit260 includes theturntable 263 on which the extensible mast 262 ismounted. The platform 270 of unit 260 is shown in FIG. 10 in variouspositions of rotation, illustrating the considerable flexibility of theunit. It will be seen that the telescoping mast 262 of unit 260 is'provided with its widest section at the bottom, whereas the telescopingmast 13 of the embodiment 10 of FIG. 1 has its narrowest section at thebottom (see FIG. 2).

Whileseveral embodiments of this invention are shown above, it will beunderstood, of course, that the invention is not to be limited thereto,since many modifications may be madewhich fall within the true spiritand scope of this invention. It is contemplated, therefore,'that anysuch modifications shall be covered by the appended claims.

I claim:

1. Overhead maintenance apparatus comprising: a

mobile base; an extensible mast mounted on said base;

means for actuating the mast upward and downward; a

platform rigidly connected to one side of'said support and rotatabletherewith.

2. Overhead maintenance apparatus comprising: a mobile base; a turntablemounted thereon for rotation relative to said base; an upstandingextensible mast mounted on said turntable;'means for actuating the mastupward and downward; a platform assembly having a supportsecured to theupper end of said mast and extend ing' horizontally therefrom, aplatform rotatably mounted on said support and spaced from said upperend of said mast a sufficient distance so that the platformwill notintersect the longitudinal axis of the mast' throughout a completerevolution of said platform.

3. Overhead maintenance apparatus comprising: a mobile base; anextensible mast mounted on said base; means for actuating the mastupward and downward; a platform having guide means extending outwardthere from; a horizontal support secured to one side of the upper end ofsaid mast, said support having side members, said guide means mounted onthe side members of said support and linearly movable relative thereto,said platformhaving a retracted position closely adjacent said upper endof said mast and an extended position spaced from said mast on one sidethereof.

4. Overhead maintenance apparatus comprising: -a mobile base; anextensible mast mounted thereon, means for actuating said mast upwardanddownward; an offset arm having one end connected to the upper end ofsaid mast; a second arm having one end pivotally connected to the otherend of said offset arm; a platform assembly pivotally connected to theother end of said second arm and rotatable therewith in a vertical planerelative to the direction of movement of said base, said platformassembly including a support pivotally connected to said other end ofsaid second arm, a platform connected to said support, .and means forrotating said platform relative'to said second arm in a horizontalplane; means for maintaining said platform in a horizontal positionparallel to the horizontal plane of the base in all degrees of rotationof said platform.

5. The apparatus of claim 4 wherein a turntable is mounted on the basefor rotation relative thereto, and the mast is mounted on the turntable.

6. Overhead maintenance apparatus comprising: a mobile base; anextensible mast mounted thereon; means for actuating said mast upwardand downward; an offset arm'having one end connected to the upper end ofsaid mast; a second arm having one end pivotally connected to the otherend of said ofiset arm; a platform assembly "ing a retracted positionclosely adjacent that end of said second arm which is attached to saidplatform assembly, and an extended position spaced from said'end'of'said second arm; means'for maintaining said platform in ahorizontal position parallel to the horizontal plane of the base in alldegrees of rotation of said platform.

7. The apparatus of claim 6 wherein a turntable is mounted on the basefor rotation relative thereto, and the mast is mounted on the turntable.

8. Overhead maintenance apparatus comprising: a mobile base; anextensible mast mounted thereon; means for actuating said mast upwardand downward; an offset arm having one end connected to the upper end ofsaid mast; a second arm having one end pivotally connected to the otherend of said ofiset arm; a platform'assembly pivotally connected to theother end of said second arm and rotatable therewith in a vertical planerelative to the direction of movement of said base, said platformassembly including a support connected to said other end of said secondarm, said support having .a horizontal portion, and a platform rotatablymounted on said 'horizontal portion and spaced from that end of saidsecond arm -which is attached to said platform assembly.

9. The apparatus of claim 8 wherein a turntable is mounted on the basefor rotation relative thereto, and the mast is mountedon theturntable.

10. Overhead maintenance apparatus comprising: a mobile base; anupstanding extensible mast mounted on said base; means for actuatingsaid mast upward and downward; a platform assembly having a supportsecured to the upper end of said mast and extending horizontallytherefrom, a platform rotatably mounted on said support and spaced fromsaid upper end of said mast a sufiicient distance so that the platformwill not intersect the longitudinal axis of the mast throughout acomplete revolution of said platform.

References Cited by the Examiner UNITED STATES PATENTS Tamini 182-62.5Mitchell 182-2 X Hotchkiss 182-2 Mitchell 182-63 Mitchell 182-63 Thym182-2 REINALDO P. MACHADO, Primary Examiner.

1. OVERHEAD MAINTENANCE APPARATUS COMPRISING: A MOBILE BASE; AN EXTENSIBLE MAST MOUNTED ON SAID BASE; MEANS FOR ACTUATING THE MAST UPWARD AND DOWNWARD; A PLATFORM ASSEMBLY HAVING A SUPPORT MOUNTED ON SAID MAST AND ROTATABLE ABOUT SAID MAST IN A HORIZONTAL PLANE AND A PLATFORM RIGIDLY CONNECTED TO ONE SIDE OF SAID SUPPORT AND ROTATABLE THEREWITH. 